Survival of the Flight Test: Airplanes Evolve, Too

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Living creatures aren't the only things capable of evolution.
Airplane designs are constantly evolving, too, a new study
suggests.

Traditionally, people have thought it impossible to witness
biological evolution, since it takes place on timescales much
longer than a single human life. However, airplanes follow the
same patterns of evolution as flying animals do, but over an
observable period of time, researchers say.

"Here we show that we can witness evolution in our lifetime by
watching the evolution of the flying human-and-machine species:
the airplane," the authors wrote in the study, detailed Tuesday
(July 22) in the
Journal of Applied Physics.

"Airplanes are flying buildings," the researchers wrote. "Every
model is a new human-and-machine design for moving our bodies,
groups and belongings over the entire globe."

The researchers found that airplanes follow the same principles
as birds, bats and other flying animals: Larger designs are
faster, more efficient and have greater flying range. Engine mass
is proportional to the airplane's mass, in much the same way that
the muscles, heart and lungs of a flying animal correspond with
its body mass. In addition, an airplane's wingspan is
proportional to fuselage length, and the amount of fuel needed is
also proportional to body size.

"This, again, is akin to what we see among the flying creatures
in nature, showing that airplanes converge [on] the architectural
design rules that unite them with their living counterparts,"
Bejan
said in a statement.

One exception to evolutionary trends among airplanes occurred
with the Concorde, a retired supersonic passenger jet jointly
built by British and French aircraft manufacturers in the 1960s.
The Concorde could fly transatlantic flights, such as from New
York to London, in less than half the time of other commercial
airliners. The Concorde was small, with a long fuselage and short
wingspan. In contrast to its predecessors, it had massive engines
and poor fuel economy, the researchers said.

Airplane design can be considered a flow system, which is
anything that has a branching pattern in its evolution, such as
river basins, animal migration routes or city traffic.In 1996,
Bejan developed a rule, known as the constructal law,which states
that "for any finite flow system to persist, that is, be alive,
it must evolve in such a way that it provides easier and easier
access to its currents."

In this case, the "living" system is the flying-man-and-airplane,
and its "currents" include properties such as the flow of the
vehicle body mass on the world map, air currents around the body,
and water and heat currents in the airplane engine, Bejan told
Live Science.

Based on this model of airplane evolution, predicting the next
phase of airplane design should be easy, the researchers said.
They foresee the creation of more larger aircraft, with engine
sizes and wingspans remaining proportional to fuselage sizes.

The findings suggest that the evolutionary process can be applied
to more than just biology, Bejan said. "Evolution belongs in
physics," he said.